# [ncl-talk] Function rcm2rgrid producing "noisy" results

Dennis Shea shea at ucar.edu
Tue Mar 22 14:08:06 MDT 2016

```The documentation and argument prototyping indicates that  latitude and
longitudes are expected. The function works on a sphere and uses distances
calculated via great circle distance formula.

function rcm2rgrid (

lat2d [*][*] : numeric,
lon2d [*][*] : numeric,
fi           : numeric,
lat      [*] : numeric,
lon      [*] : numeric,
Option       : numeric
)

Hence, this is not the appropriate function to use.
========

https://www.ncl.ucar.edu/Document/Functions/interp.shtml

There are numerous interpolation functions. Maybe

==
https://www.ncl.ucar.edu/Document/Functions/Built-in/dsgrid2.shtml
https://www.ncl.ucar.edu/Document/Functions/Built-in/natgrid.shtml
==

Still, I'm not sure if these are appropriate for doubly periodic boundary
conditions.

On Tue, Mar 22, 2016 at 11:58 AM, Michael Toy <toy at ucar.edu> wrote:

> Hello,
>
> I am using the function “rcm2rgrid” to interpolate a 2D field onto a
> Cartesian grid from a smooth non-orthogonal curvilinear grid.  Note that I
> am not on the sphere, but on an idealized flat plane with doubly periodic
> boundary conditions.  When the field, which is relative vorticity (zeta),
> is plotted in the native curvilinear coordinate, the contours are smooth.
> However, when the interpolated field is plotted, the contours appear very
> ragged.  I don’t know where the “noise” is coming from.  I’m wondering
> if “rcm2rgrid” is the appropriate interpolation function for what I’m
> trying to do.
>
> I’ve attached the *.ncl file I’m using which reads in a netcdf file with
> the data in the native curvilinear coordinate (a 3.8MB file stored on
>
>
> The interpolated data is stored to a file named “zeta_xy.troubleshoot.nc”.
> The first plot generated is zeta in the native coordinate, followed by the
> interpolated zeta, followed by a panel plot showing both fields.
>
> The version of NCL I’m using is 6.3.0.  Any help with producing smoother
> interpolated fields would be appreciated.  Thanks!
>
> — Mike
>
>
>
>
>
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